As a form of brachytherapy, yttrium-90 radioembolization (Y90-RE), also known as selective internal radiation therapy (SIRT) or trans-arterial radioembolization (TARE), exerts its locoregional tumoricidal effects by its near-pure emission of beta-particles from the radioactive decay of yttrium-90 ([Table 1]). Since its early therapeutic use for the palliative treatment of patients with advanced unresectable hepatocellular carcinoma (HCC), there has been recognition that the tumor response to Y90-RE will be dependent on the relationship between the delivered activity and dose administered. This appreciation for the importance of dosimetry also stemmed from the recognition that liver toxicity can occur due to delivering “too much dose”—specifically, the recognition of radiation-induced liver disease (RILD).[1]

Note: Of note, while beta-decay is the predominant decay for yttrium-90, every 32 per million decays result in an internal pair production (gamma decay) that produces annihilation radiation that can be imaged using conventional PET/CT or PET/MRI systems.[46]

Throughout the years, the need for accurate dosimetric analysis prior to dose delivery has been demonstrated to improve outcomes.[2] With this endeavor in mind, there have been many rapid developments within the Y90 dosimetry space. This amount of rapidly developing information has left the potential new Y90-RE user with a great deal of information to digest as they learn to “how much dose to give” and how to efficiently do so. As such, the aim of this article is to provide a central and easy-to-digest source of information for Y90-RE dosimetry. Tips and considerations, with the author's opinion whenever data are lacking, will be shared as it pertains to Y90-RE of HCC—which currently has the most published data.